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Drought Variability

Drought variability is of crucial importance not only to farmers but also to people throughout the world who rely on food and resources from a region. Unfortunately, instrumental records provide only a limited picture of the size and severity of historical droughts as well as the factors impacting drought variability throughout the world.

Tree-ring data have been used to extend records of past drought. The tree-ring reconstructions show a more complete range of drought variability than is provided by the 20th century instrumental record. The extended records are useful for placing the instrumental period droughts into a longer time frame and for evaluating the rarity of the major 20th century, 1930s, and 1950s droughts in a broader temporal context.

Palmer Drought Index Studies

Living Blended Drought Atlas (LBDA) - Version 2
The half degree gridded Jun-Aug PMDI reconstructions from Cook et al. (2010) were recalibrated using the Global Historical Climatology Network (GHCN) 5km grid PMDI data. The 5km data were first upscaled to match the original half-degree grid. The recalibration was performed using a kernel density distribution mapping (KDDM) technique outlined in McGinnis et al. (2015) using an R-package provided by Seth McGinnis. We used a 50-year recalibration period covering 1929–1978 CE. We also adjusted each grid point's mean PMDI value for the recalibration period to be zero to avoid importing wet or dry bias into the recalibration. The recalibrated data set covers the continental United States just as the GHCN instrumental data does. Since instrumental data was used for 1979–2005 CE in the Cook dataset, recalibration applied only to the years 0–1978 CE. The 1979–2017 instrumental years are filled in using the post-recalibration period values from the GHCN PMDI data. The data are available in a year per row text file, a data point per row text file, and a netCDF collection. There is also a directory of annual PMDI maps.

North American Drought Atlas
Cook et al. 2004 reconstruction of summer PDSI for most of North America using a 2.5° x 2.5° grid. Temporal coverage is 0–2003 AD. The full dataset is also available for download as a netCDF collection.